1. Field of the Invention
The present invention relates generally to an improved heat pipe structure, and more particularly to a heat pipe structure, which is able to reduce thermal impedance pressure and greatly enhance the vapor-liquid circulation of the working fluid in the heat pipe and increase the heat transfer efficiency.
2. Description of the Related Art
There is a more and more obvious trend to miniaturization of all kinds of high-performance computers, intelligent electronic devices and other electrical equipments. To catch up this trend, the heat transfer components and heat dissipation components used in these devices have also been more and more miniaturized and thinned to meet the requirements of users.
It is known that heat pipe is a heat transfer component with excellent thermal conductivity. The thermal conductivity of the heat pipe is several times to several tens times the thermal conductivity of copper, aluminum or the like. Therefore, the heat pipe is used as a cooling component and applied to various electronic devices.
As to the configuration, the conventional heat pipes can be classified into heat pipes in the form of circular tubes, heat pipes with D-shaped cross sections and flat-plate heat pipes. The heat pipes are mainly used to conduct the heat generated by the heat sources in the electronic devices and cool the heat sources. Currently, in view of easy installation and larger contact area, flat-plate heat pipes are widely used for cooling the heat sources. Following the miniaturization of the cooling mechanism, various flat-plate heat pipes are widely applied to the electronic devices for conducting the heat generated by the heat-generating components.
The conventional heat pipe structure can be manufactured by means of many kinds of methods. For example, the heat pipe can be manufactured in such a manner that metal powder is filled into a hollow tubular body and sintered to form a capillary structure layer on the inner wall face of the tubular body. Then the tubular body is vacuumed and filled with a working fluid and then sealed. Alternatively, a metal-made mesh body is placed into the tubular body. The mesh capillary structure body will naturally outward stretch and expand to attach to the inner wall face of the tubular body to form a capillary structure layer. Then the tubular body is vacuumed and filled with a working fluid and then sealed. To meet the requirements for miniaturization and thinning of the electronic devices, the heat pipe needs to be manufactured with the form of a flat plate.
The flat-plate heat pipe can achieve object of thinning. However, this leads to another problem. That is, in the flat-plate heat pipe, the metal powder is sintered to form a capillary structure layer fully coated on the inner wall face of the heat pipe. When compressing the flat-plate heat pipe, the capillary structure, (that is, the sintered metal powder or mesh capillary structure body) in the flat-plate heat pipe on two sides of the compressed faces is likely to be squeezed and damaged. In this case, the capillary structure tends to peel off from the inner wall face of the flat-plate heat pipe. This will greatly deteriorate the heat transfer performance of the thin heat pipe or even make the thin heat pipe lose its function. Moreover, although the flat-plate heat pipe can conduct the heat, after thinned and flattened, the internal capillary structure of the flat-plate heat pipe will have insufficient capillary attraction. As a result, the working fluid will block the vapor passage. Furthermore, after thinned, the area of the flow passage inside the flat-plate heat pipe is reduced so that the capillary attraction is lowered. As a result, the maximum heat transfer amount is lowered. On one hand, this is mainly because after thinned, the internal capacity of the flat-plate heat pipe is reduced and on the other hand, this is because after flattened, the central section of the flat-plate heat pipe is recessed to narrow or even block the vapor passage.
To solve the above problems existing in the conventional heat pipe, some manufacturers in this field insert a core bar into the internal chamber of the flat-plate heat pipe. The core bar is formed with a specific axial cut. Metal powder is filled into the space defined by the cut and the inner wall face of the chamber. Then the metal powder is sintered to form a capillary structure at the central section of the chamber. Then the core bar is extracted out. Then the central section of the chamber is compressed and flattened. The capillary structure thermally contacts the plane parts of the inner wall face of the chamber. In addition, voids are formed on two sides of the capillary structure in the chamber to serve as the vapor passages. Accordingly, better vapor passage impedance is achievable. However, the cross-sectional area of the capillary structure is quite narrow so that the capillary attraction is lowered. As a result, the anti-gravity thermal efficiency and heat transfer efficiency are poor.